Merge pull request #642 from jpconstantineau/linker-bss-fix-warning

updated linker script to fix recurring issue with .bss linker warning

Author: hathach

cores/nRF5/linker/nrf52_common.ld

@@ -138,7 +138,7 @@ SECTIONS
 
     } > RAM
 
-    .bss :
+    .bss ALIGN(4):
     {
         . = ALIGN(4);
         __bss_start__ = .;